Effects of SiO2Addition on Phase Transition and Microstructure Evolution of Alumina Fibers Prepared Using the Sol-Gel Method

In order to optimize the phase composition and grain size of alumina fibers, 0-3 wt% SiO2were induced to prepare alumina fibers using sol-gel method with the reaction of aluminium powder, formic acid, acetic acid, nitric acid and SiO2sol. Effects of low SiO2content on the phase transition and microstructure of alumina fibers were investigated. X-ray diffraction analysis and differential scanning calorimetry results showed that the addition of silica delayed the formation of α-Al2O3, and the phase transformation path of alumina was changed from amorphous alumina → γ-Al2O3→ α-Al2O3to amorphous alumina → γ-Al2O3→ θ-Al2O3→ α-Al2O3. Moreover, scanning electron microscopy and transmission electron microscopy results confirmed that the addition of SiO2reduced the grain size and was beneficial for the dense structure. Fine-grained dense alumina fibers composed of α-Al2O3phase and transitional alumina phase were obtained by adding 1 wt% and 3 wt% silica after sintering at 1200°C for 1 h.